Leading conservatives are trying to persuade other "conservative thinkers" to speak out against Republican presidential front-runner Donald Trump.

The National Review, one of the most influential publications in American conservative thought, is publishing a dire warning from nearly two dozen of the nation's best-known conservatives, including Glenn Beck, Bill Kristol and Andrew McCarthy.

The man leading the charge, National Review editor Rich Lowry, explained in a "Kelly File" exclusive tonight that Trump doesn't truly understand the ideals and principles that make America great.

He said true conservatives believe in things like limited government, the Constitution and liberty.

"[Those] are basically afterthoughts to Donald Trump. He almost never talks about them," Lowry said, also calling into question the fact that Trump's record is anything but consistent and conservative.

"He has been on the other side on big, hot-button, defining issues like abortion, gun control, taxes and even immigration," Lowry said.

He explained that the U.S. doesn't need a strong-arm leader with attitude, but instead someone to cut the government down to size and restore it to its rightful role.